Australia's Science Forum

Hi everyone, I need your help!

What is a compound that changes colour when heated but doesn't actually undergo a chemical reaction? It just changes colour and then as it cools it returns to the original colour. I'm having a mental blank. I haven't done this one for a few years and despite searching multiple words and phrases I can't find it on here...

Thanks and I hope you're all off to a good start this year

I just googled and found that zinc oxide changes to yellow when hot (white when cool).

Used silica gel will change colour on heating. Hydrated CuSO4 will turn from blue to white on heating due to water loss. I can't think of something that will change back on cooling apart from thermochromic dyes which I'm pretty sure schools don't usually have on hand. Good luck!

Zinc oxide changes colour at around 8000 degrees Celsius, so if you can get that organised I'd be most impressed.

I did some further googling after posting here (I had done a little bit before asking) and found that Iron (III) oxide turns black at before 500deg then back to reddish brown at room temp so I'm going to give that a go.... I can remember years ago Smiley brought it up (sometime between 2007 and 2013 when I was a lab assistant previously) but that conversation may have been deleted.

Marama T wrote: ↑06 Feb 2024, 10:36 Zinc oxide changes colour at around 8000 degrees Celsius, so if you can get that organised I'd be most impressed.

Hahaha!! Sorry, I didn't google any further than that it changes colour

elaruu wrote: ↑06 Feb 2024, 12:26

Marama T wrote: ↑06 Feb 2024, 10:36 Zinc oxide changes colour at around 8000 degrees Celsius, so if you can get that organised I'd be most impressed.

Hahaha!! Sorry, I didn't google any further than that it changes colour

Well, we have had some hot weather lately

Keep me posted, I want to know if the iron oxide works.